7. Impact of miniaturization on resonators
The equivalent circuit of a resonator can generally be represented by the following figure, where the series capacitor C1 determines the approximate range of the resonator's frequency. When the quartz blank and electrode are larger, the series capacitor C1 becomes larger, and conversely, the series capacitor C1 becomes smaller when the oscillator is miniaturized, while the series resistor R1 increases.
Therefore, compared to the old model, the value of series capacitor C1 becomes smaller (L1 and R1 values become larger) due to the reduction in chip and electrode area in the miniaturized resonator.If a miniaturized resonator is placed in the oscillation circuit originally using the old model oscillator, due to the frequency difference and the increase in series resistor R1, unstable oscillation and failure to oscillate easily occur. Therefore, it is necessary to increase the oscillation margin of the circuit that increases the proportion of resistance R1 in the miniaturized resonator (negative resistance is more than 5 times the equivalent resistance RL of the resonator under load).